Mechanical shut-off, or closure, of an injection molding gate orifice is commonly achieved using a valve stem, or pin, which is actuated via pneumatic, hydraulic or electromechanical means. The actuator may be positioned congruent with the valve stem movement or adjacent to the valve stems and connected by means of a lever mechanism, or additionally, perpendicular to the valve stem movement utilizing a wedge device.
When the actuator movement is positioned perpendicular to the valve stem movement, the force required to move the valve stem is dependent on the friction between the mating components. If using an electromechanical actuator, this frictional load will result in an additional torque requirement and higher power consumption, necessitating a larger electric motor, than if an alternative arrangement were implemented. The additional friction will also result in increased wear between components, resulting in loss of positional accuracy or in their premature failure.
A plurality of valve stems are often mounted together on a single actuation plate for simplicity of design and minimization of redundant components. Additionally, reduced pitch spacing between valve stems can be realized without individual piston actuators for each valve stem requiring proximate installations. However, in this case, disassembly for service or maintenance becomes difficult. To replace a single valve stem it will be required to remove the entire actuation plate assembly from the mold. Mold disassembly can be somewhat labor intensive, while separation of the hot runner from the mold is usually less complicated. Therefore, it is more desirable for the actuation plate and valve stems to remain with the hot runner, and then subsequently be easily removed from the hot runner as one unit.
Additionally, it is crucial that the timing, or relative position, of the valve stems be maintained throughout the entire maintenance procedure with respect to the cam slots and the cam followers of the actuation plate which travel therein. Valve stems are aligned with their respective gate orifices to within microns to ensure accurate, non-destructive engagement and any mis-adjustment due to the removal and insertion of the actuation plate process would be catastrophic to the mold. For this reason, proper alignment must be ensured throughout the entire maintenance procedure.
Because injection forces are so high, the precision of any cam follower and cam arrangement in a hot runner system is in jeopardy of being damaged due to mechanical stresses being conveyed to these components unintentionally. Any slight variation in cam follower tangency to a cam slot will affect not only the balance of the entire actuation plate assembly, but the ultimate valve stem position, which will result in premature wear of the cam followers, cams and any upstream linkages, as well as misalignment of the valve stems with the gate orifices, which will cause costly damage to both components.
U.S. Pat. No. 6,113,381 describes the use of inclined planes to translate linear actuator movement to perpendicular valve stem movement via electromechanically actuated slide blocks in diagonal grooves. These bearing surfaces must be flat and parallel and in addition to having multiple frictional contact surfaces susceptible to high wear, their requirement for a close, mating fit results in a limited ability to adjust the profile of motion of the valve stems. Additionally, the range of motion of the block-in-groove design results in a flat velocity profile precluding any variation in speed or force of valve stem travel.
While U.S. Pat. No. 7,210,922 B1 describes a valve pin activation plate, whereby a plurality of valve stems are positioned together on one plate and are simultaneously reciprocated via some method, the details of this aspect of the invention are not described nor claimed in that document.
For the foregoing reasons, the present invention is directed to overcoming one or more of the problems or disadvantages set forth above, and for providing a cam apparatus whereby a valve stem actuation plate is guided on cam followers in profiled cam slots, and which also has a method of removing the entire actuation plate from the hot runner for ease of maintenance.